Flow responsive switch with broad area contact supported by filamentary means



ET AL 3,308,254

2 Sheets-Sheet'l March 7, 1 l. J. M MAHON. JR.

FLOW RESPONSIVE SWITCH WITH BROAD AREA CONTACT SUPPORTED BY FILAMENTARY MEANS Filed June 16, 1964 N VENTORS 3 E EMWVWMUWQW immvm m a1 Q K March 7, 1967 I. J. M MAHON. JR.. ETAL 3,30

FLOW RESPONSIVE SWITCH WITH BROAD AREA CONTACT SUPPORTED BY FILAMENTARY MEANS Filed June 16, 1964 2 Sheets-Sheet 2 INVENTORS FIG 9 /RVEN J. MCMAHON JR.

LEO/v H. STUENKEL BY 1104M,

A TTORNEYS United States Patent 3,308,254 FLOW RESPONSIVE SWITCH WITH BROAD AREA C O N T A C T SUPPORTED BY FILAMENTARY MEANS Irven J. McMahon, Jr., and Leon H. Stuenkel, Painesville, Ohio, assignors to The Coe Manufacturing Company, Painesviile, Ohio, a corporation of Ohio Filed June 16, 1964, Ser. No. 375,576 8 Claims. (CI. ZOO-81.9)

This invention relates to a control instrumentality, for example, an electric switch operable by the flow of a gaseous medium, such as air.

The present device is particularly suit-able for use in dryers used in the manufacture of veneer or other like material, which depend upon the circulation of heated air at relatively low velocity through a large housing to dry the veneer or other material. If the air velocity drops below a minimum value considered safe for the proper operation of the dryer, this fact should be sensed in order to operate a warning signal or automatic control equipment for the dryer, or both. Prior to the present invention there has existed a need for a practical device for this purpose.

The principal object of this invention is to provide a novel and improved device for sensing the velocity or flow rate of a gaseous medium, such as air.

Another object of this invention is to provide such a device which is particularly adapted for sensing a rel-atively low velocity flow of air, such as in a veneer dryer.

Another object of this invention is to provide such a device whose operation is conveniently adjustable in a novel manner.

Further objects and advantages of this invention will be apparent from the following detailed description of a certain presently-preferred embodiments thereof, which are illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a perspective view of device embodying this invention;

FIGURE 2 is a plan view of the device shown in FIG. 1;

FIGURE 3 is a fragmentary top perspective view on an enlarged scale showing details of the upper end of the device shown in FIG. 1;

FIGURE 4 is a sectional view approximately on the line 4-4 of FIG. 2, with portions in elevation showing the device mounted on the top wall of a veneer dryer;

FIGURE 5 is a fragmentary elevation-a1 view of the lower part of FIG. 4 showing the parts in a ditferent operating position;

FIGURE 6 is a fragmentary" elevational view of a different embodiment of the invention;

FIGURE 7 is a plan view similar to FIG. 2, showing a further modified embodiment of the invention;

FIGURE 8 is a side elevational view of the apparatus shown in FIG. 7;

FIGURE 9 is an elevational view of the apparatus shown in FIGS. 7 and 8 looking from the right, as viewed in FIG. 8; and

FIGURE 10 is a sectional view approximately on the line 10-10 of FIG. 8.

While the invention is susceptible of various modifications and alternative constructions, it is herein shown and described as embodied in an electric switch type control instrumentality. It is to be understood, however, that there is not intention to limit the invention either to the type of control instrumentality or to the form thereof shown and described, but it is the intention to cover hereby all alternative devices falling within the practice of those skilled in the art to which the invention relates and the scope of the appended claims.

3,308,254 Patented Mar. 7, 1967 Referring first to FIGS. 1-4, the switch shown therein comprises a first set of fixed contacts 20 and 21, a second set of fixed contacts 22 and 23 spaced from the first set, and a suspended, plate or sail-like mobile contact member 24 adapted to engage the fixed contacts and thereby connect the first set 20, 21 electrically to the second set 22, 23. Normally, i.e., in the absence of a fluid flow of a predetermined velocity acting on the mobile contact member 24 from the left as viewed in FIGS. 14, the mobile contact member 24 is spaced from engagement with either set of fixed contacts. However, when the fluid flow in the direction mentioned equals or exceeds the set velocity, the mobile contact member 24 bridges the first and second sets of fixed contacts to close an electrical circuit.

Both sets of fixed contacts are supported from a mounting plate assembly 25. The mobile cont a-ct plate is suspended from this same mounting plate assembly. This mounting plate assembly comprises a rectangular top plate 26 of metal or other suitable rigid material, a marginal layer 27 of sponge rubber or the like disposed directly beneath the top plate and extending along the latters side edges around its entire periphery, a marginal middle plate 28 of meta-l or other suitable rigid material directly beneath the sponge rubber layer 27 and continguous with the latter throughout its extent, and a marginal bottom layer 29 of sponge rubber or the like directly beneath the middle plate 28 and contiguous with the latter throughout its extent. The sponge rubber layer 27, middle plate 28 and sponge rubber layer 29 are formed with aligned rectangular openings 30, 31 and 32, respectively, as best seen in FIG. 4. In use, as shown in FIG. 4, the mounting plate assembly is secured to the top wall 33 of a duct or other housing through which the air or other gaseous stream flows. This wall has an opening 34 with which the openings 30, 31 and 32 in the mounting plate assembly register. sponge rubber layer 29 is cemented to the top face of this wall. The middle plate 28 is cemented to the top of sponge rubber layer 29. The upper sponge rubber layer 27 may be cemented to both plates 26 and 28 or it may be separate from either or both of them, as desired.

Either or both sponge rubber layers 27 and 29 may be replaced by other suitable yieldable material, depending upon the temperature to which the mounting plate assembly is to be subjected.

The top plate 26 of the mounting plate assembly has a screw-threaded opening 35 (FIG. 4), which threadly receives an externally threaded fitting 36. The latter rigidly supports a rigid insulation sleeve 37, which extends vertically down into the duct through the openings 30-32 in the mounting plate assembly and the opening 34 in the duct top wall 33. A rigid elongated terminal post 38 of suitable electrically conductive material extends down through the insulation sleeve 37 and is rigidly supported thereby. At its lower end this terminal post has an integral horizontally projecting extremity which constitutes the lower fixed contact 20 of this set. The other fixed contact 21 of this set is provided by an inverted L-shaped piece which is welded, soldered or brazed to this terminal post. The fixed contacts present flat contact faces 20a and 21a, respectively, which lie in a common vertical plane extending perpendicular to the direction of the flow through the duct and disposed to the right of insulation sleeve 37, as shown in FIG. 4. The upper end of terminal post 38 projects beyond the upper end of fitting 36 and insulation sleeve 37, for connection in an electrical circuit.

The other set of fixed contacts 22 and 23'is fixedly supported in identical fashion by a vertical terminal post 39 carried by an insulation sleeve 40', which is supported by fitting 41 threadedly received in an opening 42 in the top plate 26 of the mounting plate assembly. The fixed Preferably, the bottom contacts 22 and 23 present flat contact faces 22a and 23a, respectively, spaced laterally from the contact faces a and 21a of the first set and disposed in the same vertical plane as the latter.

The mobile contact member or sail 24 is a thin, light, flat plate having relatively large area opposite major faces and is suspended from the mounting plate assembly by a laterally spaced pair of elongated, thin, readily flexible filaments 43 and 44 of suitable electrical insulation material, such as nylon. These filaments are tied in loops 43a and 44a, respectively, at their lower ends which pass loosely through corresponding holes 45 and 46 in mobile contact plate 24 close to the top corners of the latter. With this arrangement, the mobile contact plate 24 is free to pivot with respect to the filaments 43 and 44.

An adjustable plate 47, which overlies the top plate 26 of the mounting plate assembly, holds the upper ends of the filaments 43 and 44. As best seen in FIGS. 2 and 3, this plate 47 has a pair of V-shaped notches 48 and 49 in its left edge which receive and locate the upper ends of the respective filaments 43 and 44. Plate 26 of the mounting plate assembly is formed with a pair of slots 50 and 51 which are disposed beneath these notches 48 and 49, respectively, and are both elongated in a direction parallel to the fiow through the duct and perpendicular to the plane of the fixed contact faces 20a, 21a, 22a and 23a. The adjustable plate 47 also has a pair of slots 52 and 53, which are elongated parallel to slots 50 and 51. Locking screws 54 and 55 extend down through the slots 52 and 53, respectively, and are threadedly received in the top plate 26 of the mounting plate assembly. The slots in adjustable plate 47 snugly, but slidably engage these screws, so that plate 47 may be adjusted to the left or right and then clamped in place by tightening these screws.

The vertices of the respective notches 48 and 49 in adjustable plate 47 (i.e., the points where the diverging side edges of the respective notches intersect) lie in a vertical plane which extends parallel to the plane of the fixed contact faces 20a, 21a, 22a and 23a and spaced from the latter plane a distance depending upon the position of plate 47 to the right or left along the top plate 26. The filaments 43, 44 and the mobile contact plate 24 lie in substantially the same vertical plane as the vertices of notches 48 and 49 normally, that is, in the absence of fluid flow in the duct.

The adjustable plate 47 is formed with a pair of rectangular slots 56 and 57 at its right edge (FIG. 2), which are aligned with the elongated slots 50 and 51 in top plate 26. Close to these slots 56 and 57, the adjustable plate 47 has narrow diagonal slots 58 and 59 extending inward from its front and back edges, respectively. As best seen in FIG. 3, the upper end of filament 43 passes from notch 48 over the top face of the adjustable plate 47 to the rectangular slot 56, and then down beneath plate 47 and up through the diagonal notch 48, which receives it tightly. The other filament 44 extends in the same manner from notch 49 across the top of plate 47, down through rectangular slot 57, beneath plate 47 and up through the diagonal slot 59 at that edge of plate 47.

The mounting plate assembly also includes a plurality of leveling screws 60 spaced apart around its marginal edges. As shown in FIG. 4, each of these screws extends loosely down through corresponding unthreaded openings 61 in the top plate 26 and openings 62 in the sponge rubber layer 27 and is threadedly received in an opening 63 in the middle plate 28. Each leveling screw has a frusto-conical head 64 at its upper end which bears against a corresponding recess in the upper surface of top plate 26. The sponge rubber layer 27 is readily compressible, so that the top plate 26 can be leveled by tightening or loosening the several leveling screws 60. This enables the user to install the switch on a duct or housing with the terminal posts 38, 39 extending precisely vertical and with the fixed contact faces 20a, 21a, 22a and 23a lying in a common vertical plane.

With the switch installed in a duct or housing, as described, in the absence of a flow of air or other gas through the duct, the mobile contact plate 24 will be suspended vertically with one of its major faces disposed in spaced, parallel, confronting relationship to the contact faces 20a, 21a, 22a and 23a of the fixed contacts, as shown in FIG. 4. This spacing is determined by the adjustable setting of adjustable plate 47 to the left or right along the mounting plate assembly.

When a stream of air or other gaseous medium fiows through the duct from right to left in FIG. 4, perpendicular to each major face of the mobile contact plate 24, it forces plate 24 to the left. At a predetermined velocity, the force of this stream acting horizontally on mobile contact plate 24 will be suflicient to position it in engagement with the contact faces 20a, 21a, 22a and 23a of the fixed contacts, as shown in FIG. 5, thereby closing 'the switch. Throughout its movement to the left, the

mobile contact plate 24 remains substantially vertical because of its free pivotal connections to the filaments 43 and 44. The switch will remain closed as long as the air velocity remains equal to or higher than this predetermined velocity.

The four spaced, co-planar contact faces 20a, 21a, 22a and 23a stabilize the mobile contact plate 24 when the latter is in engagement with them.

The set point of the switch (i.e., the fluid velocity at which it will close) may be varied simply by adjusting the position of adjustable plate 47 to the left or right to thereby adjust the normal spacing of the suspended mobile contact plate 24 from the fixed contacts. Also, if desired, the set point may be changed by replacing the mobile contact plate 24 with one of different mass or different area.

This switch is particularly adapted for detecting a low velocity flow through a large area duct or housing. .Its set point is virtually completely determined by the major face area and the mass of the mobile contact plate 24 and the latters normal suspended spacing from the fixed contact faces. The filaments 43, 44, which provide the suspension support for the mobile contact plate, present negligible resistance to the flow through the duct, and the pivotal connections of the mobile contact plate to these filaments enable the mobile contact plate to remain vertical and perpendicular to the flow through the duct throughout its movement from its normal position (FIG. 4) to its position engaging the fixed contacts (FIG. 5).

The switch just described is particularly adapted for sensing the air flow in a veneer dryer as disclosed in United States Letters Patent No. 2,757,920 to E. P. Morris.

If desired, the switch of the present invention may be installed in a bypass duct connected across a length of the main duct to bypass a certain fraction of the total fluid flow through the main duct. This arrangement can be used for any size main duct since the switch is not mounted in the main duct.' The fluid flow through the bypass duct which is actually sensed by the switch will, of course, be proportional to the total fluid flow through the main duct.

A switch of the construction shown and described having sail or mobile member made of sheet metal and an area of approximately two square inches and weighing about 43 of a pound suspended by nylon threads or cords approximately six to eight inches long have been successfully employed in veneer dryers wherein the ve-' locity of the air or drying medium moving therethrough= was as low as 500 feet per minute and even lower.

While in the preferred embodiment of the invention shown the sail. or. mobile member closes an electric cir'- cuit and thus performs a control function, his to be understood that the sail or mobile member may be incorporated and/or used with other control instrumentalities and to perform functions other than that of making or breaking an electric circuit, for example, the mobile member may be used to intercept a light beam, vary or change the reflection of a light beam, or a beam of some other form of radiation to perform a control function. In this event, the conduit within which the sail is located could be provided with windows for the transmission of the beam or beams of radiant energy-referred to or other source of the radiation and the sensing means could be housed within the conduit. Alternatively, the sail or mobile member may be employed to actuate a proximity switch. As distinguished from being suspended by flexible filaments, the sail or mobile member could be connected to the lower end of a rigid member pivotally connected to the mounting assembly for free swinging movement relative thereto. In this event the switch contacts or other control device, such as a light beam intercepting member could be located outside of the conduit through which the gaseous drying medium is conveyed.

It will, of course, be understood that the sensitivity of the device disclosed can be increased by increasing the area of the sail or mobile member facing the direction from which the gaseous drying medium strikes the same, and/ or by surrounding the sail or mobile member by a fixed enclosure which confines and/ or directs the gaseous medium against the surface of the sail or mobile member exposed thereto.

Another embodiment of the present switch is illustrated schematically in FIG. 6. This embodiment has different sets of switch contacts which are adapted tb be closed at different fluid velocities.

A first set of contacts 70, 71 is carried by a depending arm 72, which is pivotally mounted at its upper end to a member 73, the upper end of which is cylindrical and extends upwardly through the insulating sleeve 74 corresponding with the sleeve 37 previously referred to. The upper end of member 73 is connected in an external electrical circuit (not shown). A coil spring 75 is connected under tension between switch arm 72 and a downwardly extending bracket-like portion 76 of the member 73. Bracket 76 presents an abutment 77 which limits the movement of switch arm 72 counterclockwise in FIG. 6 and normally maintains the switch arm 72 vertical. Another set of switch contacts (not shown) is resiliently mounted in the same fashion in laterally spaced relationship to the contacts 70, 71, presenting contact surfaces disposed in the same vertical plane as the contact surfaces 70a and 71a of contacts 70, 71.

Another contact 80 is carried by a rigidly mounted depending arm 81, which may be connected in another portion of the external electrical circuit. The arm 81 may be supported in a manner similar to that in which the arms 38, 39 are supported. Contact 80 presents a contact surface; 80a which is disposed to the left of the contact surfaces 70a and 71a, of the first set. Still another contact (not shown) is mounted rigidly in the same fashion as contact 80, spaced laterally therefrom, and presents a contact surface lying in a common vertical plane with the contact surface 80a.

The mobile cont-act plate 24 is suspended in spaced, confronting relationship to the just-described contacts in the same manner as described in detail with reference to FIGS. 1-4. i

When the fluid flow from right to left in FIG. 6, acting against the mobile contact plate 24', exceeds a predetermined first velocity, it exerts sufficient force on the mobile contact plate 24' to position the latter in engagement with contacts 70 and 71 and the corresponding laterally spaced pair of contacts which have contact surfaces coplanar with the contact surfaces 70a and 71a. As the fluid velocity exceeds this value, it will cause the mobile contact plate 24 to pivot the switch arm '72 clockwise against the bias of its spring 75. At some predetermined higher second velocity, the mobile contact plate 24' will also engage fixed contact and the other fixed contact having a contact surface coplanar with the contact surface 800. The switch thus closes a first circuit when the fluid flow attains a first velocity and it closes a second circuit when the fluid flow attains a second, higher velocity.

The device of the present invention may include means forprotecting the mobile contact member or sail and its suspending elements or cords from injury by particles of plywood, etc., carried in the air or gaseous drying medium employed striking thereagainst by providing the same with a suitable protective shield or housing which will, not interfere with the operation of the sail, for example, as illustrated in FIGS. 7 to 10 inclusive, which show the first embodiment of the invention described above provided with such a housing. The protective housing shown in FIGS. 7 to 10 for the sail 24 and its suspension elements 33, 44 is designated generally by the reference character 90. This housing comprises a box-like portion 91, the left-hand side of which is open, as viewed in FIG. 8, and the right-hand side of which is also open with the exception of a sheet of foraminous material, for example, screen cloth 92, extending across the same. The box-like portion 91 is connected to the underside of the plate 26 by two tubular members 93, 94 elliptical in cross section, the upper ends of which are connected to a plate 95 which plate is in turn connected to the underside of the plate 26 by suitable fasteners such as screws 96.

In order to further support the housing 90, the boxlike portion 91 may be connected to the members 37, 40, as suggested in the drawings, that is, by cutting out a portion of the top 97 of the box like portion 91 of the housing, see FIG. 10, so as to accommodate the members 37, 40, bending in an upwardly direction a part of the top 97, such as the part 98, and securing a clamping member 99 thereto as by the screw 100. As illustrated in FIG. 10, opposite ends of the clamping member 99 are arcuate and engage the left-hand sides'of the members 37 and 40, as viewed in FIGS. 8 and 10, while the right-hand sides thereof are engaged in the arcuate cutout portions of the top plate 97.

From the foregoing description of the embodiment shown in FIGS. 7 to 10, it will be apparent that the mobile contact member or sail 24, and its suspension cords 33, 44, will be protected without interfering with the action of the sail as the air, etc. which operates on the sail can pass readily through the foraminous end 92 of the boxlike housing 91.

While in the embodiment shown in FIGS. 7 to 10 inclusive, the protective housing substantially encloses the sail and its suspending elements, it will be understood that it is only necessary to protect the sides thereof facing the direction from which the gaseous medium blows, for example, all of those portions of the housing 9% to the left of the mobile contact plate 24 and its suspension cords 33, 44, as viewed in FIGS. 7 and 8, could be omitted.

While certain presently-preferred embodiments of the present invention have been described in detail and illustrated in the accompanying drawings, it is to be understood, as previously mentioned, that various other modifications, adaptations and alternative forms of construction which differ from the disclosed embodiments may be adopted without departing from the spirit and scope of this invention.

We claim: I

1. In a large area duct for conducting a low velocity gaseous medium substantially horizontally, a control instrumentality for sensing the velocity of said flow comprising:

support means adapted to be mounted on the duct;

a pair of spaced electric switch contacts;

a broad area mobile contact member shaped and dimensioned to bridge said contacts; filamentary suspension means connected to said support means and to said mobile contact member for suspending said mobile contact member in spaced confronting relationship to said contacts for movement of said mobile contact member into engagement with said contacts in response to flow against said mobile contact member toward said contacts in excess of a predetermined velocity;

and menas for adjusting the position of said support means with respect to said contacts to selectively determine the flow velocity at which the mobile contact member engages said contacts.

2. In an instrumentality for performing a control operation in response to the movement of a gaseous medium traveling at low velocity:

mounting means;

a relatively light-weight member having a relatively large area adapted to be positioned in said gaseous medium;

means connecting said member to said mounting means for free movement relative thereto;

and means at one side of said relatively light-weight member and said means connecting the same to the mounting means for free movement relative thereto shielding the same against contact by particles carried by the gaseous medium which might otherwise damage the same.

3. A switch unit comprising:

a pair of switch contacts;

means supporting said switch contacts spaced from one another;

a thin, plate-like mobile contact member shaped and dimensioned to bridge said contacts;

elongated, flexible, filamentary suspension means suspending said mobile contact member in spaced confronting relationship to said contacts for movement into engagement With said contacts in response to a predetermined fluid flow against said mobile contact member in a direction toward said contacts;

and means at one side of said relatively light-weight member and said means connecting the same to the mounting means for free movement relative thereto shielding the same against contact by particles carried by the gaseous medium which might otherwise damage the same.

4. A switch comprising:

a mounting plate assembly;

a pair of laterally spaced, rigid insulation sleeves mounted on said mounting plate assembly and extending downward therefrom;

a pair of electrically conductive terminal posts extending respectively down through said insulation sleeves;

laterally spaced fixed contacts on the lower ends of said terminal posts;

a broad area mobile contact member shaped and dimensioned to bridge said fixed contacts;

filamentary suspension means extending downward from said mounting plate assembly and suspending said mobile contact member in spaced confronting relationship to said fixed contacts for movement into engagement with said fixed contacts in response to a predetermined fluid flow against said mobile contact member in a direciton toward said fixed contacts;

and means securing the upper end of said suspension means to said mounting plate assembly.

5. A switch comprising:

a mounting plate assembly including a rigid top plate, a rigid second plate spaced below said top plate, deformable resilient material sandwiched between said plates, and a plurality of screws bearing down on said top plate and threadedly received in said second plate for leveling adjustment of said top plate;

a pair of contacts below said mounting plate assembly;

support means mounted on said top plate and carrying said contacts;

a broad area mobile contact member shaped and dimensioned to bridge said contacts;

suspension means extending downward from said mounting plate assembly and suspending said mobile contact member in spaced, confronting relationship to said contacts for movement of said mobile contact member into engagement with said contacts in response to a predetermined fluid flow against said mobile contact member in a direction toward said contacts;

and means securing said suspension means on said top plate.

6. A switch comprising:

a mounting plate assembly;

support means attached to said mounting plate assembly and extending downward therefrom;

a pair of spaced contacts carried by said support means below said mounting plate assembly;

a broad area mobile contact member shaped and dimensioned to bridge said contacts;

a pair of flexible filaments extending downward from said mounting plate assembly and suspending said mobile contact member in spaced, confronting relationship to said contacts for movement of said mobile contact member into engagement with said contacts in response to a predetermined fluid flow against said mobile contact member in a direction toward said contacts;

said mounting plate assembly having a pair of parallel slots therein which are elongated in the direction of said movement of the mobile contact member;

an adjustable plate overlying said mounting plate assembly and having notches overlying said slots;

and means for adjusting said adjustable plate lengthwise of said slots;

said filaments having their upper ends received in said notches and located thereby with respect to said pair of contacts.

7. A switch comprising:

a mounting plate assembly including a rigid top plate, a rigid second plate spaced below said top plate, deformable and resilient material sandwiched between said plates, and a plurality of leveling screws bearing down on said top plate and threadedly received in said second plate for leveling adjustment of said top plate;

a pair of laterally spaced, annular fittings threadedly mounted in said top plate;

a pair of rigid insulation sleeves carried by said fittings and extending downward therefrom below said mounting plate assembly;

a pair of electrically conductive terminal posts extending down through said insulation sleeves;

a pair of laterally spaced, fixed contacts on the lower ends of said terminal posts and presenting contact faces lying in a common vertical plane;

a substantially vertically disposed thin, plate-like, mo-

bile contact member having opposite, broad area major faces and shaped and dimensioned to bridge said fixed contacts;

a pair of flexible filaments extending downward from said mounting plate assembly and suspending said mobile contact member with one of its major faces in spaced, confronting relationship to said contact faces for movement of said mobile contact member into engagement with said contact faces in response to a predetermined fluid flow against the opposite major face of said mobile contact member in a direction toward said fixed contacts, said filaments having pivotal connections to said mobile contact member to permit the latter to remain substantially vertically disposed throughout its movement against said contact faces;

said top plate of the mounting plate assembly having a pair of parallel slots therein which are elongated in the direction of said movement of the mobile contact member;

an adjustable plate overlying said top plate and having notches overlying said slots;

and means for adjusting the position of said adjustable plate lengthwise of said slots;

said filaments having their upper ends received in said slots and located thereby With respect to said fixed contacts to thereby determine the velocity of said fluid flow required to position said mobile contact member in engagement with said contact faces.

8. A switch comprising:

a first pair of spaced switch contacts;

support means for said first pair of switch contacts, resilient means biasing said support means to position said first pair of switch contacts at predetermined positions;

a second pair of spaced switch contacts;

support means for said second pair of switch contacts positioning the latter at one side of said predetermined positions of said first pair of switch contacts;

a broad area mobile contact member shaped and di- 10 mensioned to bridge the contacts of said first pair and to bridge the contacts of said second pair;

and filamentary suspension means suspending said mobile contact member in spaced confronting relationship to said first pair of contacts at the opposite side of the latter for movement into engagement with said first pair of contacts in response to a fluid fiow of a predetermined first velocity against said mobile contact member in a direction toward said first pair of contacts and for continued movement toward said second pair of contacts against the bias of said resilient means to engage said second pair of contacts at a second, higher velocity of said fluid flow.

References Cited by the Examiner UNITED STATES PATENTS 410,502 9/1889 Donner 200-81 X 1,009,338 11/1911 Perkins 200-81 1,230,787 6/1917 Robison et al 200-61 X 1,513,361 10/1924 Airey 20081 2,503,581 4/1950 French 200-81 BERNARD A. GILHEANY, Primary Examiner.

H. M. FLECK, G. MAIER, Assistant Examiners. 

1. IN A LARGE AREA DUCT FOR CONDUCTING A LOW VELOCITY GASEOUS MEDIUM SUBSTANTIALLY HORIZONTALLY, A CONTROL INSTRUMENTALITY FOR SENSING THE VELOCITY OF SAID FLOW COMPRISING: SUPPORT MEANS ADAPTED TO BE MOUNTED ON THE DUCT; A PAIR OF SPACED ELECTRIC SWITCH CONTACTS; A BROAD AREA MOBILE CONTACT MEMBER SHAPED AND DIMENSIONED TO BRIDGE SAID CONTACTS; FILAMENTARY SUSPENSION MEANS CONNECTED TO SAID SUPPORT MEANS AND TO SAID MOBILE CONTACT MEMBER FOR SUSPENDING SAID MOBILE CONTACT MEMBER IN SPACED CONFRONTING RELATIONSHIP TO SAID CONTACTS FOR MOVEMENT OF SAID MOBILE CONTACT MEMBER INTO ENGAGEMENT WITH SAID CONTACTS IN RESPONSE TO FLOW AGAINST SAID MOBILE CONTACT MEMBER TOWARD SAID CONTACTS IN EXCESS OF A PREDETERMINED VELOCITY; AND MEANS FOR ADJUSTING THE POSITION OF SAID SUPPORT MEANS WITH RESPECT TO SAID CONTACTS TO SELECTIVELY DETERMINE THE FLOW VELOCITY AT WHICH THE MOBILE CONTACT MEMBER ENGAGES SAID CONTACTS. 